A capacity estimation technique for JPEG-to-JPEG image watermarking

In JPEG-to-JPEG image watermarking (J2J), the input is a JPEG image file. After watermark embedding, the image is JPEG-compressed such that the output file is also a JPEG file. In this paper, we use the human visual system (HVS) model to estimate the J2J data hiding capacity of JPEG images, or the maximum number of bits that can be embedded in JPEG-compressed images. Watson's HVS model is modified to estimate the just noticeable difference (JND) for DCT coefficients. The amount of modifications on DCT coefficients is limited by JND in order to guarantee the invisibility of the watermark. Our capacity estimation method does not assume any specific watermarking method and thus would apply to any watermarking method in J2J framework.